1. Field of the Invention
The present invention relates to the field of radio communication technologies. More particularly, the present invention relates to an apparatus and a method for feeding back data receiving status.
2. Description of the Related Art
A Long Term Evolution (LTE) system transmits data based on Hybrid Automatic Repeat Request (HARQ), i.e., a data receiver will send receiving status feedback information of Acknowledgement (ACK) or Non-Acknowledgement (NACK) according to the corresponding data receiving status. Scheduling information for dynamic downlink data transmission is transmitted through a Physical Downlink Control Channel (PDCCH), whereas except for Semi-Persistent Scheduling (SPS), initial transmission scheduling information for downlink data does not need to be transmitted through the PDCCH, and only at the time of retransmission of the downlink data, the scheduling information needs to be transmitted through the PDCCH.
For an LTE Time Division Duplexing (TDD) system, when the number of downlink subframes is larger than that of uplink subframes, receiving status feedback information for the data of multiple downlink subframes needs to be transmitted collectively in the same uplink subframe. One of the methods for the feeding back is to perform an “AND” operation on the receiving status feedback information for the downlink subframes that transmit data, so as to obtain receiving status feedback information of one bit for each code word. Because the downlink data transmission is scheduled dynamically through a PDCCH, and User Equipment (UE) may not be able to receive a PDCCH transmitted from a base station, there may be inconsistencies between the receiver and transmitter in the method of performing an “AND” operation according to code word. To address this problem, a Downlink Assignment Index (DAI) is used in the LTE TDD system to indicate the serial number of the current downlink subframe in the radio frame that transmits the PDCCH, so that the UE can detect whether a PDCCH in the downlink subframes has been lost. For a radio frame with 4 downlink subframes, the value of the DAI may be 1, 2, 3 and 4.
There is, however, a problem with the above method, i.e., a case in which the last several PDCCHs are lost cannot be detected. In the LTE TDD, therefore, it is specified that the UE needs to feed back receiving status feedback information on a receiving status feeding-back channel corresponding to the last one downlink subframe that receives a PDCCH, so that the base station can get aware of whether the UE has lost the PDCCHs of the last several downlink subframes from the channel on which the UE feeds back the receiving status feedback information.
In a Long Term Evolution-Advanced (LTE-A) system, a Carrier Aggregation (CA) technology has been used to support a higher transmission rate, in which two or more Component Carriers (CC) are aggregated to obtain a larger working bandwidth. For example, to support a bandwidth of 100 MHz, 5 CCs of 20 MHz may be aggregated. Based on CA, the base station transmits downlink data to the UE on two or more CCs. Correspondingly, the UE also needs to support the receiving status feedback information for the downlink data received from the two or more CCs.
According to the current results of discussions on LTE-A, at most 4 bits of ACK/NACK transmission can be supported based on the technology of channel selection. In LTE-A Frequency Division Duplexing (FDD), the method of channel selection actually supports only two CCs and at most 2 bits of ACK/NACK information can be fed back on each CC. Taking a 4-bit table as an example, for a Primary CC (PCC) and a Secondary CC (SCC) employing cross-CC scheduling, the two ACK/NCK channels are obtained by scheduling PDCCHs for downlink data transmission. For example, assuming the minimum CCE index of PDCCH is n, the two ACK/NACK channels may be obtained through mapping by using an LTE method from CCE indexes n and n+1. For a SCC not employing cross-CC scheduling, the two ACK/NACK channels are configured by the higher layer, and the flexibility in assignment may be increased through an ACK/NACK Resource Indicator (ARI). According to the current results of discussions, a 4-bit mapping table as shown in FIG. 3 is employed in an FDD system. Here, ACK/NACK channels 1 and 2 correspond to the two ACK/NACK bits of a PCC sequentially and ACK/NACK channels 3 and 4 correspond to the two ACK/NACK bits of a SCC sequentially. In the table of FIG. 3, the feature that the two ACK/NACK channels always are present at the same time on or absent at the same time from the same CC is utilized to optimize the performance. Another 4-bit mapping table is as shown in FIG. 12. Here, only when some ACK/NACK information is ACK, the ACK/NACK channel corresponding thereto is selected for transmission. The only exception is that to take full advantage of the feedback capabilities of M (M is equal to 2, 3 or 4) ACK/NACK channels, when the first piece of ACK/NACK information is NACK and the remaining pieces of ACK/NACK information are all NACK or Discontinuous Reception (DRX), a Quadrature Phase-Shift Keying (QPSK) constellation point of the first ACK/NACK channel may be used for the indication. The method as illustrated in FIG. 12 may be applied to the scenario in which the 4 ACK/NACK bits and the corresponding ACK/NACK channels are all independent of one another.
In the tables, N denotes NACK, A denotes ACK, D denotes DRX and the symbol “/” denotes “or”.
For an LTE-A TDD system, in a case of supporting CA, the UE needs to feed back significantly more bits of receiving status feedback information than in single carrier transmission. For example, when a radio frame has 4 downlink subframes for transmitting data and 5 CCs, assuming Multiple Input Multiple Output (MIMO) data transmission is configured for the UE, 40 bits of receiving status feedback information need to be fed back. Apparently, if the method of feeding back receiving status feedback information for single carrier is also used, many uplink overheads will be occupied and the uplink coverage area will be reduced. Moreover, all the uplink control channels currently supported in an LTE system cannot support so large an amount of receiving status feedback information. If it needs to support 40 bits of feedback, the structure of feeding-back channels needs to be redefined, which significantly increases the complexity of standardization.
Therefore, a need exists for an apparatus and a method for feeding back data receiving status, so as to reduce the uplink overheads occupied by the receiving status feedback information and increase the uplink coverage area.